Why these tiny rainforest frogs have evolved to show off their beating hearts

Nature · Published 3 October 2026 Swipe more like this →

In short: Glass frogs are small, nocturnal amphibians found in the New World tropics that possess a startling biological trait: translucent skin on their undersides. This transparency allows observers to see their internal organs, including the heart pumping blood, but scientists believe this feature serves a vital purpose in their survival.

Belonging to the family Centrolenidae, these tree frogs inhabit vegetation near streams from tropical lowland forests to mountain regions. While their transparency is their most famous trait, it is not universal across all 160 species. For those that are translucent, the effect acts as a form of camouflage. By softening the edges of the frog against its background—a phenomenon known as edge diffusion—the animal becomes harder for predators to detect against the varying light and shadows of a leaf.

The reproductive behavior of these frogs is equally specialized. Males are fiercely territorial, using squeaking calls and wrestling to defend their leafy perches. Once a female deposits her eggs on the underside of a leaf, she typically departs, leaving the male to perform guard duty. He remains with the clutch 24/7, protecting the developing embryos from threats like wasps, which he may physically kick away. In some species, the spotted patterns on the frogs' backs are thought to mimic the appearance of egg masses, potentially confusing predators.

The evolutionary history of the Centrolenidae is complex, with research suggesting they originated in South America before dispersing into Central America. Their classification has been a subject of ongoing debate among herpetologists, with recent phylogenetic studies shifting their placement closer to the family Leptodactylidae. While they are masters of their environment, these frogs face modern pressures, as habitat fragmentation and climate change increasingly threaten their survival in the wild.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Why the red-eyed tree frog uses a startling flash of red to survive
• How glass frogs use sleep to become nearly invisible to predators
• Why the chemicals on a frog's skin could revolutionize human medicine
• Why the red-eyed tree frog uses neon colors to trick its predators
• How a South American frog uses natural sunscreen to survive the heat
• The Blue-gray Gnatcatcher is a tiny, restless acrobat that builds nests from spiderwebs
• Why these giant rodents are the world's most effective land mine detectors
• The tiny, suction-cupped fish that thrives in almost every corner of the ocean
• The giant petrel is the only seabird of its family that walks on land
• The goblin shark uses a terrifying, elastic catapult to snatch prey in the dark.
• The giant otter shrew is a master of the river, but no true shrew.
• The godwit is a champion of endurance, flying thousands of miles without a single stop.

More in Vertebrates · More in Nature · Latest · A–Z · All topics